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Masahiko Ohtaka1, Katsuhiko Takagi1, Hidesada Natsui2, Tatsuya Arai1, and Shinichi Yoda1
1National Space Development Agency of Japan, Sengen 2-1-1, Tsukuba-city, Ibaraki 305-8505, Japan
2Advanced Engineering Services Co. Ltd., Takezono 1-6-1, Tsukuba-city, Ibaraki 305-0032, Japan
The experimental results obtained in 2000 are significant for the thermocapillary convection of a low Pr fluid. We have succeeded in detection of the transition to oscillatory flow by the surface temperature measurement without any flow disturbances. The first and clear experimental evidence for the transition from the steady flow to the oscillatory one was found by the non-contact temperature measurement of a molten tin surface (Fig. 1) and the surface flow visualization (Fig. 2 and Movie). Validity of the experimentally determined Mac2 and the frequency of the standing wave were confirmed by comparing with a numerical result by Imaishi et al.
The effect of an aspect ratio (As) on the Mac2 has been investigated (Fig. 3). The Mac2 increases with decreasing As in the range of As ≤ 1.24. Internal temperature field of typical case at oscillatory flow was speculated by the phase relation analysis of the simultaneous multi-measurement data of surface temperature. The numerical simulation was conducted under the same conditions of the experiment in order to check the onset point and temperature fluctuation data obtained by the experiment.
The surface tension of molten tin was measured at various temperatures between 523 and 1023K under the oxygen partial pressures (PO2) between 10-19 and 10-6 Mpa (Fig. 4). It was clarified an appropriate value of the surface tension coefficient for the experimental chamber is -0.9 x 10-4 N/mK. It was also found that the temperature coefficient of surface tension at a constant PO2 raised as PO2 increased, and the sign of the coefficient changed from minus to plus at log PO2= -9.375MPa.
Visualization technique (3D-UV) of flow field measurements for liquid metals using ultrasonic transducer with high heat resistance has been successively developed for the experiments. Sensitivity of transducer was examined at high temperature condition same as actual thermocapillary experiment (Fig. 5). High spatial resolution was obtained in the direction of wave propagation(Fig. 6). Visualization performance of ongoing sensor-design was confirmed by numerical simulation. The tracer is also currently under development. Technique for improvement of sphericity and surface roughness was developed (Fig. 7). Endurance against molten tin (Fig. 8) and acoustic characteristics (Fig. 9) of trial production were experimentally examined.
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